JPH062163A - Production of stainless steel for porcelain enameling - Google Patents

Abstract

PURPOSE:To easily provide a stainless steel with high adhesion to porcelain enamel with certainty by regulating the surface of a stainless steel to specific surface roughness and then treating this stainless steel at specific temp. in a nonoxidizing gas atmosphere of specific due point. CONSTITUTION:The surface of a stainless steel is regulated so that surface roughness Ra becomes 1.0-3.0mum, by which grooves for eating porcelain enamel can be formed in the surface of the stainless steel. Subsequently this stainless steel is heat-treated at 650-1100 deg.C in a nonoxidizing gas atmosphere of -30 to -5 deg.C dew point. It is preferable to regulate heat treatment time to about 30-120sec in the case where this heat treatment is done, e.g. by using a continuous annealing furnace. By this method, an extra thin and dense oxide film can be formed on the surface of the stainless steel and the stainless steel for porcelain enameling having high adhesion to porcelain enamel can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing enamel stainless steel, which is capable of producing enamel stainless steel having high adhesion to enamel.

[0002]

2. Description of the Related Art Generally, the adhesiveness of enamel whose base metal is steel is that, for example, by heat-treating a base metal whose surface is sandblasted, components in the base metal are oxidized to form a surface oxide. It is generated by the chemical bonding between the surface oxide and the glassy layer formed by heat treatment of the glaze.

However, when the base metal is stainless steel, the adhesion to the glassy layer is insufficient only by sandblasting, so a method of forming an extremely thin intermediate layer on the surface of stainless steel is usually adopted. Has been done. As a concrete method, there are a chromate treatment, a chemical coloring method, a plating and the like as a chemical method, and a heat treatment performed under various atmospheres as a physical method. Among these intermediate layer forming methods, it is known that the heat treatment method is particularly effective for the adhesion of enamel.

By the way, in the manufacturing of enamel products up to now, after the forming process of steel is finished, the formed product is subjected to pretreatment such as sand blasting → washing with water → chemical conversion treatment. It is conceivable to apply the pretreatment, which also employs heat treatment by controlling the atmosphere, to the molded product whose base is stainless steel.

[0005]

However, when the above pretreatment is applied to a stainless steel molded product, the molded product is heat treated in an atmosphere regardless of whether a batch processing furnace or a continuous processing furnace is used. It is physically extremely difficult to provide a molded product with sufficient adhesiveness with enameled, and even if sufficient adhesiveness can be obtained, there is a problem that it takes a long time to economically impose a heavy burden. .

The present invention has been made to solve the above-mentioned conventional problems, and is a method for producing a stainless steel plate for enamel, which can easily and surely give high adhesion to enamel to stainless steel. The challenge is to provide.

[0007]

The present invention provides a method for producing enamel stainless steel by heat treating stainless steel to produce enamel stainless steel, wherein the surface of the stainless steel has a surface roughness Ra of 1.0 μm or more. After adjusting so as to be in the range of 3.0 μm, the stainless steel is heated to 650 ° C.
The said subject was achieved by processing in a non-oxidizing gas atmosphere whose dew point is -30 to -5 degreeC.

[0008]

As described above, stainless steel differs from mild steel in that
Since it has a passivation film on its surface, when enameled, partially dissolved iron in mild steel forms an oxide film on its surface, which serves as an intermediate layer and secures adhesion to enamels. On the other hand, in stainless steel, this elution phenomenon is unlikely to occur, so that sufficient adhesion with enamel cannot be obtained.

As a result of various investigations by the present inventors for improving the adhesiveness of enamel with respect to a stainless steel molded product, it has been found that an oxide film is formed by heat treatment at the stage of the material before the molding process. Is also effective from above,
It was found that the oxide film exhibits excellent enamel adhesion by treating stainless steel in a low oxidizing atmosphere to form an extremely thin and dense film.

The present invention has been made on the basis of the above findings, and the surface roughness Ra of the stainless steel surface is 1.0 μm.
After adjusting so as to fall within the range of m to 3.0 μm, the stainless steel was heated at 650 ° C. to 1,100 ° C. and had a dew point of −.
It is characterized in that the treatment is carried out in a non-oxidizing gas atmosphere at 30 ° C to -5 ° C. In the present invention, the stainless steel includes a steel strip having a continuous shape and a steel sheet having a predetermined size and shape.

The specific structure of the present invention will be described in detail below with reference to an example in which a cold-rolled steel strip of stainless steel is targeted.

The surface of the stainless steel strip has a surface roughness R
It is adjusted so that a is in the range of 1.0 μm to 3.0 μm. This Ra is the center line average roughness, and a portion of the measurement length L is extracted from the roughness curve in the direction of the center line, the center line of this extracted portion is the X axis, and the direction of longitudinal magnification is the Y axis. When the roughness curve is shown as y = f (x), the following (1)
The value obtained by the equation is expressed in micrometers (μm).

[0013]

[Equation 1]

When Ra <1.0 μm, the groove formed by the unevenness of the surface is too small, so that the effect of biting the enamel into the groove is reduced and the adhesiveness of the enamel is lowered.
When Ra> 3.0 μm, the appearance of the enamel is poor because the texture of the enamel is rough and the enamel easily peels off when external force is applied to it. .

The surface roughness Ra before the oxidation treatment is 1.0 μm.
It is shown in FIG. 1 that sufficient enamel adhesion is obtained when ≦ Ra ≦ 3.0 μm. In FIG. 1, the horizontal axis represents the surface roughness Ra expressed on a logarithmic scale, and the vertical axis represents the Erichsen value after enamel. In the same figure, the results are shown when treated at 900 ° C. for 120 seconds in a non-oxidizing gas atmosphere having a dew point of −15 ° C., and an Erichsen value of 6.0 mm or more is acceptable.

The adjustment of the surface roughness is performed, for example, in the case of a cold-rolled steel strip made of stainless steel by transferring it to the stainless steel strip at the time of cold finish rolling by using a work roll having fine irregularities on the surface. You can Note that the surface roughness can be adjusted by using another method such as a sandblast method.

The cold-rolled stainless steel strip, the surface roughness of which has been adjusted as described above, is heat-treated while passing through a continuous bright annealing line. The atmosphere of this annealing furnace has a dew point of -30 ° C to -5.
It is formed of non-oxidizing gas between ℃ and the temperature of the furnace is 65
The temperature is 0 ° C to 1,100 ° C.

Here, examples of the non-oxidizing gas include hydrogen gas, nitrogen gas, and inert gas such as argon. These non-oxidizing gases may be used as a mixture or may be used alone.

FIG. 2 shows the relationship between enamel adhesion, dew point and furnace temperature. The shaded area in FIG. 2 is an extremely effective treatment range in which sufficient enamel adhesion can be obtained within 2 minutes. In addition, under the condition outside the square region, the enamel adhesion was insufficient.

As described above, the dew point of the atmospheric gas is -30 °.
Or less than -5 ° C, the enamel adhesion is insufficient, and when the atmospheric gas is less than 650 ° C or more than 1,100 ° C, the adhesion is similarly insufficient. Met.

The heat treatment time in the continuous annealing furnace under the above conditions according to the method of the present invention is preferably 30 seconds to 120 seconds. The reason is that if the oxide film becomes abnormally thick, the adhesion to the enamel will deteriorate, or
This is because bubbles or pits may be generated in the enamel and the appearance quality may be significantly impaired.

The heat treatment can also be carried out in a batch system. When processing in a batch furnace, the stainless steel strip is wound loosely and charged. It is preferable that the heat treatment time at that time is raised after gas replacement and the holding time at the predetermined temperature is up to 15 minutes at the maximum.

Examples of stainless steel to which the method of the present invention can be applied include austenitic stainless steel such as SUS304L, ferritic stainless steel such as SUS430, and duplex stainless steel. Particularly, in the case of the above austenitic stainless steel, C ≦ 0.03
A low carbon content of 0% is preferable, and other components in this case are Si ≤ 1.00%, Mn ≤ 2.00%, S ≤ 0.03.
0%, P <0.040%, Ni 16.00 to 15.00
%, Cr 16.00 to 25.00%, and further added to these components are, for example, Cu = 4.00% and Mo.
≦ 4.00 may be added.

[0024]

EXAMPLE An example according to the present invention will be described in detail below.

0.8 mm thick stainless steel strip (SUS3
04L) is rolled by a work roll whose surface is roughened at the time of finish rolling during cold rolling, thereby transferring the above-mentioned uneven shape to the surface of the steel strip to obtain a surface roughness Ra 1.
The thickness was adjusted to 5 μm, and subsequently, the plate was passed through a continuous bright annealing line, and a part of the sheet was cut, and the plate was heat-treated in a batch type heating furnace.

Table 1 shows the results of the above heat treatment performed under different conditions. In addition, in Table 1, the results by the conventional method are also shown for comparison. The adhesion of enamel was evaluated by the Erichsen test. In addition to the batch type heating furnace, heat treatment was also performed in a continuous bright annealing furnace under almost the same conditions, but the Erichsen value Er exceeded the acceptable value of 6.0 mm, and it was almost the same as the batch type. There was no difference.

[0027]

[Table 1]

From Table 1 above, according to the method of the present invention, it was possible to obtain enamel adhesiveness comparable to or higher than that of the conventional method in an extremely short time. Therefore, in the case of molding using the material produced by the method of the present invention, simply removing stains before baking enamel, surface roughening by sandblasting etc. after molding, heat treatment requiring a long time is not required. The enamel process can be greatly shortened. Moreover, the adhesion of the enamel can be significantly improved and the uniformity of quality can be improved.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, the heat treatment does not necessarily have to be continuously carried out in a continuous bright annealing furnace or the like, but may be carried out batchwise.

[0031]

As described above, according to the present invention, it is possible to easily and surely give high adhesion to enamel to stainless steel.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the surface roughness of stainless steel and the adhesiveness of enamel.

FIG. 2 is a diagram showing the correlation between the enamel adhesion of stainless steel and the dew point and heat treatment temperature.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yuji Sone 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Takeshi Higashi 2-3-3 Uchisaiwai-cho, Chiyoda-ku, Tokyo No. Kawasaki Steel Co., Ltd., Tokyo Head Office (72) Inventor Nobutaka Yukawa 1-2-1, Shiginohigashi, Joto-ku, Osaka City, Osaka Prefecture Takara Standard Co., Ltd. (72) Inventor Masakazu Akamatsu Kagino, Joto-ku, Osaka City, Osaka Prefecture Higashi 1-chome 2-1 Takara Standard Co., Ltd.

Claims (1)

[Claims] 1. A method for producing enamel stainless steel by heat treating stainless steel to produce enamel stainless steel, wherein the surface roughness Ra of the surface of the stainless steel is 1.0 μm.
After adjusting so as to be in the range of 3.0 μm, the stainless steel was heated at 650 ° C. to 1,100 ° C. and the dew point was −30.
A method for producing stainless steel for enamel, which comprises treating in an atmosphere of non-oxidizing gas of ℃ to -5 ℃.